In addition to the points mentioned above, Professional also has the following features and services:

-Support for Dynamic Disks. This allows software implementation of RAID, which could be useful for a system with multiple hard drives.
-Encrypting File System – Allows for filesystem-level encryption. Not as secure as BitLocker, which is only available in Ultimate.
-Location Aware Printing
-Presentation Mode – Lets you change the behavior of Windows while giving presentations, i.e. control volume, display different wallpaper, prevent screensaver from appearing, etc.
-Group Policy – Allows you to control just about all aspects of the Windows operating system locally or via Windows Server 2003/2008
-Offline Files and Folder Redirection – Again, more a feature of a Windows machine joined to a domain
-Ability to join a Windows domain – Home Premium cannot join Windows domains
-Windows XP Mode – Allows you to run Windows XP SP3 inside Windows 7. Used for compatibility with older programs.
-Software Restriction Policies